installing sub floors

Old 12-07-03, 07:08 PM
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Question installing sub floors

Question: How to install a sub floor over an 100 yr old plaster ceiling so that when walking on it, the ceiling will not crack?

The floor goes on top of the rafters of my unfinished attic

One idea I thought of:

Sandwitch a rubber mat between two 1/2" screwed down plywood sub floors. The mat will act as a shock absorber.

Do I need to do anything? Could the ceiling be attatch to some type of frame seperated from the rafters?

I would like to do this job my self
Any Ideas?
Old 12-08-03, 10:53 AM
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Most of the cracking is caused by joist deflection. If the joists are over-spanned or not designed to bear weight they will flex as you walk and can cause cracks. Adding foam or anything else will not stiffen the joists. What is the span of the rafters and what is their height?

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